Extruded plastic lumber and method of manufacture

ABSTRACT

A composite reinforced plastic lumber article, such as a board or a plank having a generally rectangular cross-section, is formed by extruding a wood particle/polymer composition through an extrusion die which forms a corrugated or relatively thin sheet cross-section core part. The core part is compressed to push corrugations closer together and then cooled in a two-stage cooling process with water spray and submersion followed by vacuum and air blast drying of the article, followed by extruding an outer coating of the same composition over the core part. A continuous plank-like composite article is thus formed and is cooled after the outer coating is extruded over the core part. Opposed surfaces of the article may be embossed to provide a woodgrain appearance. The two-stage article forming process provides more rapid cooling of the material to enhance the speed of production of reinforced plastic lumber articles and the like.

BACKGROUND OF THE INVENTION

[0001] Structural composite lumber or so-called plastic wood productshave been developed in recent years wherein the composite structures arecharacterized by reinforced polymer compositions. So-called plasticlumber, for example, has been developed wherein wood fibers or woodflour is mixed with polymer materials, such as polypropylene orpolyethylene, to form a composition which can be extruded intostructural shapes, including conventional sizes and shapes of lumber.The advantages of such types of plastic lumber include high strength,rot resistance and ease of fabrication.

[0002] However, one disadvantage of prior art composite shapescomprising so-called plastic wood or plastic lumber, is competitivecosts resulting from the cost of raw material but primarily resultingfrom the speed with which the so-called plastic wood shapes can befabricated as compared with conventional lumber. Wood flour or woodparticle/polymer compositions must be heated to substantial temperaturesto perform extrusion processes required to form the structural shapes ofplastic lumber. The speed of plastic lumber manufacturing processes hasnot, in many instances, been sufficient to make plastic lumbercompetitive with conventional lumber due to the relatively slowextrusion speeds required to allow the temperature of plastic or similarcomposite articles to be reduced to a level which will permit finalfabrication and storage in an economical manner.

[0003] For example, the cross-sectional thickness of most types ofconventional plastic lumber shapes is such that heat transfer from thecore portion of the article being manufactured is not sufficient toallow finish processing of the article at a speed which is costcompetitive with conventional lumber. Polymer materials used infabricating conventional plastic lumber or plastic wood shapes have arelatively low heat transfer rate and the core temperature ofconventional plastic lumber shapes remains too high to permit processingof the material at a competitive rate. However, in accordance with thepresent invention an improved composite or plastic lumber article isprovided which is fabricated by an improved process, also in accordancewith the invention.

BRIEF SUMMARY OF THE INVENTION

[0004] The present invention provides a composite or so-called plasticwood or plastic lumber article which may be fabricated in selectedconventional cross-sectional shapes and dimensions. The presentinvention also provides an improved method for fabricating extrudedcomposite structural articles, such as so-called plastic lumber.

[0005] In accordance with one aspect of the present invention, acomposite, extruded lumber or extruded plastic wood article is providedwhich may be of a conventional cross-sectional shape, that is arectangular cross-sectional shape of standard lumber dimensions, andwhich is characterized by a corrugated composite core part encapsulatedin an outer layer of composite material to form a conventionalcross-sectional shape of standard lumber dimensions, for example. Theplastic lumber article may be fabricated using an extrudable polymermaterial which is reinforced by a wood particle or wood flour filler.The extruded plastic lumber articles may also be fabricated using othertypes of filler or reinforcement materials, such as glass fibers orother reinforcing fibers. Metal foil or sheet may also be encapsulatedin or comprise part of the extruded plastic lumber article.

[0006] In accordance with another aspect of the invention, conventionallumber shaped articles are provided which include a corrugated coreportion of composite material encapsulated within an outer layer ofcomposite material and which are fabricated in a way which increases thespeed of production of the articles. By way of example, a compositeplastic board of a type used as a conventional fence picket may befabricated by extruding a corrugated core part, cooling the core partand compressing the corrugations toward each other and thenencapsulating the core part within an outer layer of material to form aso-called plastic lumber article having conventional cross-sectionaldimensions of board width and thickness. Moreover, the composite lumberarticle may be cut to any specified length in a conventional manner andmay be otherwise worked in the same manner as a conventional woodstructural article.

[0007] The present invention further contemplates a method offabricating composite or reinforced polymer structural articles, such asconventional lumber shapes, by extruding a reinforced plastic core partfrom a first extrusion die, cooling the core part and then encapsulatingthe core part by extruding an overlay of the same or similar compositematerial to form the final dimensions of the article. The time requiredto fully fabricate the article and to cool the article to a temperaturewhere it may be worked further or placed in storage without anydeleterious effects is minimized as compared with prior art methods.

[0008] In a preferred embodiment, a core part of the article is extrudedfrom a first extrusion die as a corrugated, or zigzag cross-sectionalshape, or is subsequently formed into such a shape to provide for rapidcooling of the extrudate, initially. The corrugated shape is compressedand guided by respective sets of guides to bring the folds orcorrugations substantially contiguous with each other, after initialextrusion and cooling, and so as to maintain the desired flatness andsize of the core shape prior to further working. The continuous extrudedand compressed core part is then subjected to further cooling via aliquid spray, followed by submersion of the core part in cooling liquid,normally water, as it is being pulled from the extruder. The core partis guided through the cooling liquid spray by spaced apart sets of guiderollers to maintain flatness and sizing of the core part.

[0009] The continuous composite core part of the article is then passedthrough a dryer comprising a vacuum chamber and pressure air blowers toremove moisture from the core part. In a preferred arrangement of theprocessing apparatus, the core part is then passed through a conveyortype puller apparatus characterized by opposed endless belts which gripand traverse the core part along a fabrication path.

[0010] In accordance with a further aspect of the present invention, thecomposite extruded core part of the structural article is then passedthrough a second die wherein a coating of a second composition,preferably the same as the core part, is applied over the core part tocompletely encapsulate the core part. The article may then be passedthrough a set of rollers for final sizing of the article cross-sectionalshape to provide sharp edges and flat surfaces, for example. Thecontinuous article, after sizing, enters an elongated cooling troughfilled with cooling liquid, preferably water, followed by exit from thecooling trough and passage through an air blast curtain to remove waterfrom the surface of the cooled and finished article. Prior to cooling,the article may be passed through one or more sets of embossing rollersto emboss the outer surfaces of the article to provide a woodgrainappearance, for example. Still further, a continuous belt-type pullingapparatus may be disposed downstream, in the direction of movement ofthe continuous extrudate, from the cooling water trough. The continuousfinished composite lumber article may then be cut to length by aconventional sawing apparatus.

[0011] The composition of the article of the present invention may besomewhat varied. Conventional polymers used for extruded shapes may beused in forming the article and such polymers may be reinforced byvarious reinforcement materials including wood fibers, wood flour andfibers of other compositions including glass, carbon and the like.

[0012] Those skilled in the art will further appreciate theabove-mentioned advantages and superior features of the inventiontogether with other important aspects thereof upon reading the detaileddescription which follows in conjunction with the drawing.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0013]FIG. 1 is a perspective view showing a portion of a core part ofan extruded composite or plastic lumber article in accordance with theinvention;

[0014]FIG. 2 is a cross-section of a finished composite or plastic woodor lumber article in accordance with the invention;

[0015]FIG. 3 is a general schematic diagram of a system for forming theextruded composite or plastic lumber article in accordance with theinvention;

[0016]FIG. 4 is a detail perspective view of a set of guide rollers forcompressing and guiding the corrugated core part of the article of thepresent invention;

[0017]FIG. 5 is a detail plan view in somewhat schematic form of thefirst stage liquid cooling apparatus for the system shown in FIG. 3;

[0018]FIG. 6 is a detail perspective view of the second stage extrusiondie for the system shown in FIG. 3;

[0019]FIG. 7 is a detail perspective view showing a portion of theprocess of fabricating an alternate embodiment of an article accordingto the present invention;

[0020]FIG. 7A is a cross section view of the finished article shown infabrication in FIG. 7; and

[0021]FIG. 8 is a perspective view, in somewhat schematic form,illustrating a further alternate embodiment of an article, system andmethod in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] In the description which follows, like parts are markedthroughout the specification and drawing with the same referencenumerals, respectively. The drawing figures are not necessarily to scaleand certain features may be shown in somewhat schematic form in theinterest of clarity and conciseness.

[0023] Referring to FIGS. 1 and 2, there is illustrated a compositeplastic wood or lumber article in accordance with the invention andgenerally designated by the numeral 20, FIG. 2. The article 20 is, byway of example, characterized as a generally rectangular cross-sectionplank or board which may have suitable dimensions for a finishedstandard lumber article for use as fence pickets. Those skilled in theart will recognize that various cross-sectional dimensions of width andthickness may be provided in fabricating various types of composite orplastic lumber articles, and the like, in accordance with the invention.

[0024] As shown in FIGS. 1 and 2, the plastic lumber article 20 includesa core part 22 formed of continuous folds or corrugations 24. Thecorrugations 24 are shown in FIG. 1 spaced apart and adjacent each otherto leave opposed relatively shallow elongated parallel valley portionsor recesses 26 on opposite sides 28 and 30 of the core part. FIG. 2further shows the plastic lumber article 20 with an outer coating 32,which completely encapsulates the core part 22 and provides finished,opposed, parallel spaced apart, outer surfaces 34 and 36 and opposed,finished, parallel and spaced-apart outer surfaces 38 and 40 forming aconventional rectangular cross-section lumber article in accordance withthe invention. The cross-section thickness of the corrugations of thecore part 22 may vary from about 0.060″ to about 0.200″. For a lumberarticle having a width of about 3.20 inches and a thickness of about0.40 inches delimited by surfaces 38 and 40 and surfaces 34 and 36,respectively, the thickness of the corrugations 24 is preferably about0.085″.

[0025] The plastic or composite lumber article 20 may be formed ofdifferent compositions. For example, a preferred composition is amixture of about 75% polypropylene and 25% wood flour, by weight.However, the reinforcing material may be other than wood flour includingwood fibers, glass fibers, carbon fibers or other reinforcing fibers orparticles, for example. The polymer material may also comprisepolyethylene or another selected polymer. However, for purposes ofgeneral applications of conventional lumber articles, theabove-mentioned wood flour/polypropylene composition is one which ispreferred.

[0026] Referring now to FIG. 3, a system for fabricating the compositeor plastic lumber article 20 is illustrated and generally designate bythe numeral 42. The system 42 includes a first extruder 44 of a typecommercially available, such as a single or twin screw extruder by DavisStandard of Pawcatuck, Conn. Extruder 44 is adapted to receive materialprepared for forming the core part 22 of article 20 by way of a suitablefeeder hopper 46. The raw material used for fabricating the article 20may comprise, for example, preformed pellets of 25% wood flour and 75%polypropylene polymer by weight. Extruder 44 is adapted to extrude theheated polymer/wood flour composition to an extruder dischargetemperature of about 380° F., for example. The core portion or part 22is formed by an extrusion die 48, which is mounted on the extruder 44 ata suitable discharge opening for the heated composition described above.The die 48 includes a die orifice having a cross-sectional shapecorresponding to the shape of the corrugated core part 22 wherein thecorrugations 24 are spread further apart than in the finished articleshown in FIG. 2.

[0027] As the heated plastic material is extruded from the die 48 toform core part 22, it traverses a short distance unsupported and then ispreferably guided by apparatus 49, including opposed sets of guiderollers 49 a and a set of support rollers 49 b, see FIG. 4 also, tocompress the corrugations or folds 24 closer together so that thegrooves or valleys 26 are substantially eliminated to approximate thefinished core part 22, as shown in FIG. 2. In other words, thecorrugations 24 are moved together or contiguous with each other asshown in FIG. 2.

[0028] As the heated core material is extruded through the die 48 intoambient atmospheric conditions at normal room temperature, some coolingeffect takes place before any guide rollers described above compress thecorrugations 24 closer together, thanks to the decreased thickness andincreased surface area of the core part 22 provided by the corrugations24. However, the continuous extruded core part 22 then enters agenerally rectangular box-like, elongated cooling tank 52, FIGS. 3 and5, in which spaced-apart sets of water spray nozzles 53 are arranged toeject a water spray on at least top and bottom sides of the core part.Spaced apart sets of opposed guide rollers 54 a and 54 b are suitablymounted within the tank 52 for supporting the continuous core part 22 asit is extruded from the extruder 44 and to guide and support the corepart to maintain its final cross-section dimension. For example, thecore part 22 may not be substantially reduced in thickness after it isextruded from the extruder 44 but is reduced in width by compressing thecorrugations 24 closer together at the apparatus 49 wherein the width isreduced to approximately 55% of the width of the core part exiting theextruder die 48.

[0029] As the continuous extruded core part 22 is passed through thetank 52, the temperature of the core part is reduced to about 200° F. Asecond liquid coolant tank 55, FIG. 3, is mounted adjacent the dischargeend of tank 52 and is adapted to guide the continuous core part 22therethrough while submerged in a water bath 55 a. Spaced-apart sets oftop and bottom and side-to-side guide rollers, not shown, may beprovided in the tank 55 to provide further guidance and support for thecontinuous extrusion of the core part 22 as it passes through the tank55.

[0030] Referring further to FIG. 3, the system 42 provides for removingmoisture from the core part 22 as it exits tank 55, including anapparatus 56, which includes a generally rectangular hollow plate or box56 a, including an elongated vacuum chamber or slot 57 formed therein.Apparatus 56 is suitably connected to a source of vacuum 56 b so that,as the core part 22 passes through the box 56 a, moisture on the corepart is evaporated and withdrawn therefrom. A suitable array of opposedair blast nozzles 56 c may also be provided, see FIG. 3, and connectedto a source of pressure air, not shown, for assisting in the removal ofwater from the surfaces of the core part 22 before it passes into thevacuum chamber or slot 57 of apparatus 56.

[0031] The somewhat firm and cooled core part 22 is then passed througha device 60, FIG. 3, including opposed motor driven endless conveyorbelts 62 between which the core part 22 is disposed and engaged by fortraversing the core part in timed relationship to the rate at which theextruder 44 is extruding the core part therefrom, so that the continuouscore part 22 will not buckle or be stretched out of its preferred shape.

[0032] Referring still further to FIG. 3, the system 42 includes asecond extruder apparatus 66 including an extruder die 68, see FIG. 6also, into which the core part 22 is extended. The extruder 66 alsoincludes a coating material receiving hopper 69 for receiving rawcoating material in pellet form, for example, preferably having the samecomposition as the material used to form the core part 22. Flowablecoating material is injected into die 68 via conduit means 68 b, FIG. 6,to completely envelope core part 22 with material which becomes coating32, FIG. 2. As the core part 22 passes through the extruder die 68, thecoating 32 is applied thereover to completely encapsulate the core partand to form the opposed surfaces 34, 36, 38 and 40. For the dimensionsof the article 20, the coating is confined to a thickness ofapproximately 0.10″.

[0033] Extruded article 20, now having the opposed finished surfaces 34,36, 38 and 40 formed thereon, may then be passed through an apparatus70, FIG. 3, including opposed rollers 72 and 74 which have suitable diesurfaces thereon to provide embossing on surfaces 34 and 36, forexample, to simulate woodgrain, if desired. Other decorative or texturedsurfaces may be provided by modified rollers similar to the rollers 72and 74. The rollers 72 and 74 are preferably water cooled to providesome further cooling of the article 20 as it exits the extruder die 68.

[0034] After passing through the apparatus 70, the extruded article 20is also passed through an apparatus 49 d, similar to apparatus 49 andincluding a set of opposed rollers 49 a and a second set of opposedrollers 49 b for final sizing of the article to provide substantiallyflat and parallel surfaces 34 and 36 and 38 and 40, respectively.Apparatus 49 d is substantially like apparatus 49, FIG. 4, but mayinclude opposed sets of rollers 49 b above and below article 20.Alternatively, apparatus 49 d may include only opposed sizing rollers 49a. The positions of rollers 49 a and 49 b are adjusted to accommodatethe preferred dimensions of article 20.

[0035] After passing through the sizing roller sets for apparatus 49 das just described, the continuous extruded article 20 is passed througha further cooling apparatus 78, FIG. 3, comprising an elongated waterfilled tank for final cooling of the article. Article 20 is preferablysubmerged in a cooling water bath 78 a in tank 78. Upon exiting the tank78, continuous article 20 is subjected to an air blast from an array ofair jet nozzles 82 or the like, FIG. 3, to remove further moisture fromthe surfaces of the article. Continuous feeding of the article 20through the system 42 is aided by a second traversing apparatus 60 ahaving opposed motor driven endless belts 62 which are spaced apartsufficiently to engage surfaces 34 and 36, respectively, to feed thecontinuous article 20 at the same speed as the core part 22 is being fedby the apparatus 60. Lastly, a controllable power saw 90 may be disposeddownstream of the apparatus 60 a for sawing the article 20 intopredetermined lengths as the article 20 is ejected from the feed ortraversing apparatus 60 a.

[0036] Thanks to the construction of the composite plastic wood orlumber, article 20, as illustrated and described, the core part 22 ofthe article and coating 32 are cooled faster than if the entirecross-section of the finished article were formed in one extrusionoperation. In this way, production speeds for extruding and finishingthe article 20 may be increased. For an article 20 having the dimensionsand composition described herein, the speed at which the article 20 istraversed through the system 42 shown and described may be in a range ofabout fifteen feet per minute to one hundred fifty feet per minute.Accordingly, by forming the core part 22 in the manner shown anddescribed and, cooling same to a substantially reduced temperature, thenextruding an overlay of reinforced polymer to encapsulate the core partand then cooling the finished article, an improved high strengthcomposite plastic wood or lumber article may be fabricated efficientlyand with a speed of manufacture sufficient to be cost competitive withconventional milled wood products. However, the composite plastic lumberarticle 20 enjoys all of the advantages of polymer based, or so-calledplastic products.

[0037] Referring to FIGS. 7 and 7A, a second embodiment of a compositeplastic article in accordance with the invention is illustrated andgenerally designated by the numeral 21. The article 21 includes a corepart 22, formed in the same manner as the core part for the article 20,and adapted to be encapsulated within an outer layer 32 a, FIG. 7A, ofcomposite material of the same composition. However, the composite orso-called plastic lumber article 21 also includes one or opposed layers35 of metal foil, preferably aluminum, adapted for overlying theopposite sides 28 and 30 of the core part 22, contiguous therewith andencapsulated by the aforementioned coating or outer layer 32 a. Thealuminum foil overlays or layers 35 are preferably perforated atperforations 35 a, FIG. 7, over their entire surface to provide for thearticle outer layer or coating 32 a to be contiguous with the surfacesof the core part 22 to form a suitable chemical and mechanical bondthereto. Accordingly, the composite or plastic lumber article 21 inaccordance with the invention enjoys the benefits of the article 20 butis of enhanced strength due to the metal foil or sheet overlays 35encapsulated between the coating or outer layer 32 a and the core part22. The overlays 35 may also be formed in such a way as to enhance theappearance of the article 21 as well as its strength, particularly ifthe outer layer or coating 32 a is relatively clear and free ofreinforcement materials dispersed throughout.

[0038] Referring now to FIG. 8, another embodiment of the invention isillustrated wherein a plastic lumber article core part 22 b is formed byextruding a thin rectangular sheet 22 c of the same material as thatwhich forms the core part 22. Sheet 22 c is extruded from a modifiedextruder die 48 a adapted to be associated with the extruder 44 in placeof the die 48. Extruder die 48 a thus forms a thin rectangular crosssection sheet 22 c which is then forced to form corrugations 24 a.Corrugations 24 a may be formed initially by traversing the sheet 22 cover one or more sets of knife edge rollers 23, one set shown in FIG. 8,so as to crease the sheet 22 c to begin forming the corrugations 24 a.The corrugations 24 a are further developed by passing the sheet 22 cthrough an apparatus 149 having opposed guide rollers 149 a engageablewith opposite sides of the sheet 22 c. Suitable support rollers 149 bare provided to guide and support the core part 22 b. Second and thirdstage corrugation forming apparatus 151 and 153 may be provided, asshown in FIG. 8, to further develop and compress the corrugations 24 auntil the core part 22 b is formed substantially like the core part 22,as shown in FIG. 2. Once the core part 22 b is formed with itscorrugations 24 a fully compressed to be contiguous with each other, thecore part has been substantially cooled from its temperature at the exitof extruder die 48 a. Core part 22 b may be subjected to furtherprocessing to form an article 20 in the same manner as described abovefor the embodiment wherein the core part 22 is initially formed withcorrugations 24 by the extruder die 48.

[0039] One advantage of forming the core part 22 b in the mannerdescribed above is that further cooling of the core part may take placebefore it is finally compressed, since the relatively thin sheet 22 cwill have its entire surface area exposed to cooling air circulation orother cooling fluids before the corrugations 24 a are fully formed andcompressed.

[0040] Preferred embodiments of an extruded, composite or plastic lumberarticle, a system for fabricating same and a method of fabricating samein accordance with the invention are believed to have been described insufficient detail herein to enable one skilled in the art to practicethe invention. Although an extruded composite or plastic wood or lumberarticle in accordance with the invention, as well as a system and methodfor the fabrication or formation thereof have been provided as describedherein, those skilled in the art will recognize that varioussubstitutions and modifications may be made to the articles 20 and 21,the system 42 and modifications thereto and the method described abovewithout departing from the scope and spirit of the invention as setforth in the appended claims.

What is claimed is:
 1. An extruded plastic lumber article comprising: acore part formed of a polymer material and having a cross-section whichis compressed after extrusion through an extrusion die; and a polymercoating disposed over the surfaces of said core part to encapsulate saidcore part to form said article.
 2. The article set forth in claim 1wherein: said core part is formed to have a cross-section comprisingrepeated corrugations between one side of said core part and an oppositeside of said core part.
 3. The article set forth in claim 1 wherein:opposed surfaces of said coating are embossed.
 4. The article set forthin claim 1 wherein: the composition of said core part and said coatingcomprises one of polypropylene and polyethylene.
 5. The article setforth in claim 1 wherein: the composition of one of said core part andsaid coating comprises one of reinforced polyethylene and polypropylene.6. The article set forth in claim 5 wherein: said one of saidpolypropylene and polyethylene is reinforced by wood particles.
 7. Thearticle set forth in claim 6 wherein: the composition of said core partand said coating comprises about 25% wood flour and 75% polypropylene,by weight.
 8. A plastic lumber article comprising: a core part having across section comprising repeated corrugations extending between oneside of said core part and an opposite side of said core part, said corepart being formed of a reinforced polymer; and a coating disposed overthe surfaces of said core part to encapsulate said core part, saidcoating being formed of one of a polymer and a reinforced polymer. 9.The article set forth in claim 8 wherein: said corrugations arecompressed to be substantially contiguous with each other.
 10. Thearticle set forth in claim 8 wherein: said core part is reinforced bywood particles dispersed throughout said core part.
 11. The article setforth in claim 8 wherein: said article is reinforced by at least onesheet of metal foil disposed between said core part and said coating.12. The article set forth in claim 8 wherein: said coating is reinforcedby wood particles.
 13. The article set forth in claim 8 wherein: thecomposition of said core part and said coating comprises one of woodparticles dispersed in polypropylene or polyethylene.
 14. The articleset forth in claim 8 formed by a process which includes: extruding saidcore part; cooling said core part after extrusion thereof; and extrudingsaid coating over said core part.
 15. The article set forth in claim 8formed by a process which includes: compressing said corrugations to besubstantially contiguous with each other before encapsulating said corepart in said coating.
 16. The article set forth in claim 15 formed by aprocess which includes: cooling said core part after compressing saidcorrugations.
 17. The article set forth in claim 16 formed by a processwhich includes: passing said core part though a water spray to cool saidcore part.
 18. The article set forth in claim 16 formed by a processwhich includes: supporting at least opposite sides and a third side ofsaid core part by support rollers while cooling said core part.
 19. Thearticle set forth in claim 8 formed by a process which includes:providing an embossing on at least one surface of said article afterdisposing said coating over said core part.
 20. The article set forth inclaim 8 formed by a process which includes: cooling said article afterdisposing said coating on said core part by passing said article in acontinuous extrudate thereof through a quantity of cooling liquid. 21.The article set forth in claim 20 formed by the process which includes:blowing pressure air over said article after removal of said articlefrom said cooling liquid to remove liquid from the surfaces thereof. 22.The article set forth in claim 8 formed by a process which includes:passing said core part through a vacuum chamber before disposing saidcoating over said core part.
 23. The article set forth in claim 8 formedby a process which includes: pulling said article through an extruder toapply said coating.
 24. The article set forth in claim 8 formed by aprocess which includes: pulling said article through a set of embossingrollers and a cooling liquid tank with a pulling apparatus engaged withsaid article at a point downstream of said tank in the direction ofmovement of said article.
 25. A method for forming an extruded plasticlumber article comprising a core part formed of a reinforced polymermaterial encapsulated by a coating of a polymer material disposed overthe surfaces of said core part, said method comprising the steps of:forming said core part to have a cross section comprising repeatedcorrugations extending between one side of said core part and anopposite side of said core part; cooling said core part after formationthereof; extruding said coating over said core part to form saidarticle; cooling said article to reduce the temperature thereof; andcutting said article into discrete lengths.
 26. The method set forth inclaim 25 including the steps of: compressing said corrugations towardeach other after forming said corrugations.
 27. The method set forth inclaim 26 including the steps of: cooling said core part with a coolingliquid after compressing said corrugations.
 28. The method set forth inclaim 27 including the steps of: supporting said core part by supportroller means while cooling said core part.
 29. The method set forth inclaim 27 including the step of: applying a vacuum to said core partafter cooling said core part to remove moisture therefrom.
 30. Themethod set forth in claim 27 including the step of: blowing pressure airover said core part to remove cooling liquid from the surfaces thereof.31. The method set forth in claim 25 including the step of: embossing atleast one surface of said article after extruding said coating over saidcore part.
 32. The method set forth in claim 25 including the step of:cooling said article after extruding said coating by passing saidarticle in a continuous extrudate thereof through a quantity of coolingliquid.